In classical black-and-white photography a photographic element containing a silver halide emulsion layer coated on a transparent film support is imagewise exposed to light. This produces a latent image within the emulsion layer. The film is then photographically processed to transform the latent image into a silver image that is a negative image of the subject photographed. The resulting processed photographic element, commonly referred to as a negative, is placed between a uniform exposure light source and a second photographic element, commonly referred to as a photographic paper, containing a silver halide emulsion layer coated on a white paper support. Exposure of the emulsion layer of the photographic paper through the negative produces a latent image in the photographic paper that is a positive image of the subject originally photographed. Photographic processing of the photographic paper produces a positive silver image. The image bearing photographic paper is commonly referred to as a print.
In a well known, but much less common, variant of classical black-and-white photography a direct positive emulsion can be employed, so named because the first image produced on processing is a positive silver image, obviating any necessity of printing to obtain a viewable positive image. Another well known variation, commonly referred to as instant photography, involves imagewise transfer of silver ion to a physical development site in a receiver to produce a viewable transferred silver image.
In classical color photography the photographic film contains three superimposed silver halide emulsion layer units, one for forming a latent image corresponding to blue light (i.e., blue) exposure, one for forming a latent image corresponding to green exposure and one for forming a latent image corresponding to red exposure. During photographic processing dye images that are complementary subtractive primaries--that is, yellow, magenta and cyan dye images are formed in the blue, green and red recording emulsion layers, respectively. This produces negative dye images (i.e., blue, green and red subject features appear yellow, magenta and cyan, respectively). Exposure of color paper through the color negative followed by photographic processing produces a positive color print.
In one common variation of classical color photography reversal processing is undertaken to produce a positive dye image in the color film (commonly referred to as a slide, the image typically being viewed by projection). In another common variation, referred to as color image transfer or instant photography, image dyes are transferred to a receiver for viewing.
In each of the classical forms of photography noted above the final image is intended to be viewed by the human eye. Thus, the conformation of the viewed image to the subject image, absent intended aesthetic departures, is the criterion of photographic success.
With the emergence of computer controlled data processing capabilities, interest has developed in extracting the information contained in an imagewise exposed photographic element instead of proceeding directly to a viewable image. It is now common practice to extract the information contained in both black-and-white and color images by scanning. The most common approach to scanning a black-and-white negative is to record point-by-point or line-by-line the transmission of a near infrared beam, relying on developed silver to modulate the beam. In color photography blue, green and red scanning beams are modulated by the yellow, magenta and cyan image dyes. In a variant color scanning approach the blue, green and red scanning beams are combined into a single white scanning beam modulated by the image dyes that is read through red, green and blue filters to create three separate records. The records produced by image dye modulation can then be read into any convenient memory medium (e.g., an optical disk). The advantage of reading an image into memory is that the information is now in a form that is free of the classical restraints of photographic embodiments. For example, age degradation of the photographic image can be for all practical purposes eliminated. Systematic manipulation (e.g., image reversal, hue alteration, etc.) of the image information that would be cumbersome or impossible to achieve in a controlled and reversible manner in a photographic element are readily achieved. The stored information can be retrieved from memory to modulate light exposures necessary to recreate the image as a photographic negative, slide or print at will. Alternatively, the image can be viewed as a video display or printed by a variety of techniques beyond the bounds of classical photography--e.g., xerography, ink jet printing, dye diffusion printing, etc.
Hunt U.K. 1,458,370 illustrates a color photographic element constructed to have three separate color records extracted by scanning. Hunt employs a classical color film modified by the substitution of a panchromatic sensitized silver halide emulsion layer for the green recording emulsion layer. Following imagewise exposure and processing three separate records are present in the film, a yellow dye image recording blue exposure, a cyan dye image recording red exposure and a magenta dye image recording exposure throughout the visible spectrum. These three dye images are then used to derive blue, green and red exposure records, but the photographic element itself is not properly balanced to be used as a color negative is classically used for photographic print formation.
One of the common techniques for improving the speed-granularity relationship of an image produced in a silver halide photographic element is to provide multiple (usually two or three) superimposed silver halide emulsion layers differing in speed (i.e., differing in their threshold sensitivities). By coating the fastest of the emulsion layers to receive imagewise exposing radiation first, the effective speed of the fastest layer is increased without increasing its granularity. Hellmig U.S. Pat. No. 3,846,135 discloses fast over slow emulsion layer arrangements in black-and-white photographic elements while Eeles et al U.S. Pat. No. 4,184,876 and Kofron et al U.S. Pat. No. 4,439,520 disclose similar arrangements in color photographic elements, the latter also providing a background explanation of speed-granularity relationships.